Apparatus and method of detecting endpoint of a dielectric etch

ABSTRACT

A system detects the clearing of a dielectric at a plurality of contact sites by measuring the surface voltage of the dielectric and comparing the surface voltage to a reference voltage set to a value that relates to the cleared contact sites. Another system detects the clearing of a dielectric at a plurality of contact sites on a substrate by measuring the rate of change of a substrate current during an etch process and ending the etch process when the rate of change is approximately zero. Another system detects the clearing of a dielectric at a contact site by measuring a substrate current during an etch process and ends the etch process when the measured substrate current exceeds a predetermined value.

TECHNICAL FIELD OF THE INVENTION

[0001] This invention relates to the field of semiconductormanufacturing, and more particularly, to the field of etchingdielectrics.

BACKGROUND OF THE INVENTION

[0002] Types of dielectrics used in semiconductor manufacturing includeoxides, nitrides, borophosphosilicate glasses (BPSG), silicon-dioxides,silicon-nitrides, and tetra-ethyl-ortho-silicates (TEOS). During anintegrated circuit manufacturing process, these dielectrics are oftenetched. For example, insulating oxides are etched, protective oxides areetched, and sacrificial oxide masks are etched. Dielectrics sometimesfunction as insulators to isolate one level of conductors and devicesfrom another. However, the conductors and devices on different levelsmust be interconnected in order to have a working integrated circuit.This is accomplished by etching holes in the dielectric layers in orderto connect one layer to another. In the art of integrated circuitmanufacturing, these etched holes are referred to as contacts or vias.In this document, all holes etched in a dielectric are referred tosimply as contacts.

[0003] A long standing problem in the art of manufacturing integratedcircuits is that of completing a process step and not knowing whetherthe process step completed successfully. If the step did not completesuccessfully, and the processing of the integrated circuit continues,then it is likely that at the end of the manufacturing process thecircuit will not work as designed. Thus, continued processing after afailed process step results in wasting the costs of processing after thefailed step.

[0004] In the etching of dielectrics, a problem that can cause aprocessing step to fail is the failure of the process to completely etchthe dielectric at a contact location. This failure prevents devices frombeing connected. One approach to solving this problem is to design theetching process to over etch, i.e., to run the process longer thannecessary for etching some contacts in order to completely etch allcontacts on the substrate. One difficulty with this approach is thatover etching results in some contacts being etched to dimensions largerthan necessary, and this interferes with the important goal ofintegrated circuit manufacturing of increasing the density of thedevices on a substrate.

[0005] For these and other reasons, there is a need for the presentinvention.

SUMMARY OF THE INVENTION

[0006] The present invention provides a system and method for overcomingthe problems as described above and others that will be readily apparentto one skilled in the art from the description of the present inventionbelow.

[0007] A system in accordance with one embodiment of the presentinvention for use in identifying the successful completion of adielectric etching process on a semiconductor substrate includes avoltage probe for measuring the surface voltage of the dielectric, aselectable reference voltage, and a comparator. The selectable referencevoltage is set to a value related to the surface voltage of thedielectric when the contacts are cleared of the dielectric. Thecomparator is coupled to the selectable reference voltage and thevoltage probe. The comparator compares the measured voltage to theselectable reference voltage and produces an endpoint detection signal.

[0008] In one embodiment of the system, the voltage probe is anon-contact probe. In another embodiment of the system, the selectablereference voltage is set to a value approximately equal to the surfacevoltage of the dielectric when the contacts are cleared of thedielectric. In still another embodiment, the comparator is an analogcomparator, and in yet another embodiment, the comparator is a digitalcomparator.

[0009] A method in accordance with one embodiment of the presentinvention for identifying the completion of a dielectric etching processon a semiconductor substrate includes the steps of setting a selectablereference voltage to a value related to the surface voltage of thedielectric when a contact is cleared of the dielectric, measuring thesurface voltage of the dielectric, comparing the measured voltage to theselectable reference voltage, and identifying the successful completionof the dielectric etching process by noting when the measured voltage isless than the selectable reference voltage.

[0010] In one embodiment of a method of the present invention, theselectable reference voltage is set to a value of approximately equal tothe surface voltage of the dielectric when the contacts are cleared ofthe dielectric. In another embodiment, measuring the surface voltage ofthe dielectric consists of averaging multiple measurements of thesurface voltage of the dielectric.

[0011] A method for etching a dielectric on a semiconductor substrate ina plasma etch system is also described. The method includes placing asubstrate with a dielectric to etch within a plasma etch chamber,setting a selectable reference voltage to a value related to the surfacevoltage of the dielectric when the contact is cleared of the dielectric,etching the dielectric in the plasma etch chamber, measuring the surfacevoltage of the dielectric, generating an endpoint detection signal whenthe measured voltage is less than the selectable reference voltage,detecting the endpoint detection signal, and stopping the etching whenthe endpoint detection signal is detected.

[0012] In one embodiment of this method, the selectable referencevoltage is set to a value approximately equal to the surface dielectricvoltage when the contact is cleared of the dielectric.

[0013] In another embodiment, a method for etching a dielectric on asemiconductor substrate in a plasma etch system includes placing asubstrate with a dielectric to etch within a plasma etch chamber,setting a selectable reference current to a value related to thesubstrate current when the contact is cleared of the dielectric, etchingthe dielectric in the plasma etch chamber, measuring the substratecurrent, generating an endpoint detection signal when the measuredcurrent is greater than the selectable reference current, detecting theendpoint detection signal, and stopping the etching process when theendpoint detection signal is detected.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a block diagram of a system in accordance with thepresent invention in which the contact dielectric etching is incomplete.

[0015]FIG. 2 is a block diagram of a system in accordance with thepresent invention in which the contact dielectric etching is complete.

[0016]FIG. 3A is a graph showing the relationship between the dielectricsurface voltage and the selectable reference voltage for an area of asemiconductor substrate that has not been completely etched and an areaof the semiconductor substrate that has been completely etched.

[0017]FIG. 3B is a graph showing the endpoint detection signal in anunetched area and an etched area.

[0018]FIG. 4 is a general flow diagram of the endpoint detection processof the present invention.

[0019]FIG. 5 is a general flow diagram of a second embodiment of theendpoint detection process of the present invention.

[0020]FIG. 6 is a general flow diagram of a method for real timedetection of the endpoint of a dielectric etching process in a plasmaenvironment of the present invention.

[0021]FIG. 7 is an illustration of a measurement system for measuringthe surface voltage of a semiconductor substrate in a plasma etchchamber using a voltage probe.

[0022]FIG. 8A is an illustration of a system for sensing a substratecurrent in a substrate having partially etched contacts.

[0023]FIG. 8B is an illustration of a system for sensing a substratecurrent in a substrate having etched contacts.

[0024]FIG. 8C is an graph of a substrate current versus time for aplasma etch process of a substrate.

DETAILED DESCRIPTION OF THE INVENTION

[0025] In the following detailed description, reference is made to theaccompanying drawings which form a part hereof, and in which is shown byway of illustration specific embodiments in which the invention may bepracticed. These embodiments are described in sufficient detail toenable those skilled in the art to practice the invention, and it is tobe understood that other embodiments may be utilized and thatstructural, logical and electrical changes may be made without departingfrom the spirit and scope of the present invention. The followingdetailed description is, therefore, not to be taken in a limiting sense,and the scope of the present invention is defined by the appendedclaims.

[0026] Embodiments of systems and methods in accordance with the presentinvention shall be described with reference to FIGS. 1-8. Theembodiments of the systems and methods of the present invention foridentifying the completion of a dielectric etching process on asemiconductor substrate are useful whenever contacts are etched in adielectric, and determining whether the contacts are cleared of thedielectric is desired. Embodiments of the present invention can also beused in connection with processes that make use of protective oxides.sacrificial oxides, nitrides, borophosphosilicate glasses (BPSG),silicon-dioxides, silicon-nitrides, and tetra-ethyl-ortho-silicates(TEOS).

[0027] As shown in FIG. 1, in one embodiment of the present inventionsystem 100 comprises voltage probe 110, selectable reference voltage120, and comparator 130.

[0028] Voltage probe 110 measures surface voltage 140 of dielectric 150on semiconductor substrate 155 after a dielectric etching process. Asone skilled in the art will recognize, any device that can sense surfacevoltage 140 of dielectric 150 is suitable for use in the presentinvention. In one embodiment, a non-contact Kelvin Probe is used tosense surface voltage 140. A Kelvin Probe is a non-contact,non-destructive vibrating capacitor device used to measure the workfunction difference, or for non-metals, the surface potential, between aconducting specimen and a vibrating tip. Kelvin Probes are known topractitioners in the art of integrated circuit manufacturing.

[0029] A reference voltage, such as selectable reference voltage 120 isset to a value that corresponds to surface voltage 140 of dielectric 150when contact site 160 is cleared of the dielectric during an etchingprocess. The precise value for a given manufacturing step can bedetermined by measuring surface voltage 140 of dielectric 150 at thecompletion of a dielectric etching process and then verifying thatcontact site 160 is cleared of the dielectric using a scanning electronmicroscope. The precise value of the selectable reference voltage candepend on the physical parameters of the etching process, such as theinitial depth of dielectric 150, the number of contact sites 160 indielectric 150, and the aggressiveness of the etching process. In atypical process, with a dielectric thickness of one thousand angstroms,selectable reference voltage 120 can have a value of between one-halfvolt and two volts.

[0030] Comparator 130, in one embodiment, is coupled to voltage probe110 and selectable voltage reference 120 for the purpose of generatingendpoint detection signal 170 shown as a time-voltage magnitude graph.Comparator 130, in one embodiment, is an analog device with an analogoutput, and compares the voltage measured by voltage probe 110 withselectable reference voltage 120. Endpoint detection signal 170indicates whether the voltage measured by voltage probe 110 is greaterthan or less than selectable reference voltage 120. In an alternateembodiment, comparator 130 is an analog integrated circuit comparator.In another embodiment, comparator 130 is a digital comparator. In stillanother embodiment, comparator 130 is a person who compares the surfacevoltage indicated by voltage probe 110 to selectable voltage reference120. The digital comparator can be implemented in a microprocessor, as acombination of hardware and software, or strictly in hardware. An analogcomparator is preferable when voltage probe 110 and selectable referencevoltage 120 generate analog voltage output signals, a digital comparatoris preferable when selectable reference voltage 120 and voltage probe110 generate digital output signals, and a human comparator ispreferable when voltage probe 110 provides a visual displays of thevoltages or a visual display of the relationship between the voltages.

[0031]FIG. 2 shows the system of FIG. 1 with like components labeledwith like reference numerals. A difference between FIG. 1 and FIG. 2 isthat in FIG. 1 contact site 160 is not cleared of the dielectric, whilein FIG. 2 contact site 260 is cleared of the dielectric. Anotherdifference is that surface voltage 240 of FIG. 2 has a value differentfrom the value of surface voltage 140 of FIG. 1. Still anotherdifference is that FIG. 2 shows endpoint detection signal 270 as atime-voltage magnitude graph assuming a positive voltage level, whichindicates that contact 260 is cleared of the dielectric. Whereas, FIG. 1shows endpoint detection signal 170 assuming a low voltage level,indicating that contact 160 is not cleared of the dielectric.

[0032]FIG. 3A shows in graphical form the relationship between surfacevoltage 140 of FIG. 1 and selectable reference voltage 120 in an area ofa semiconductor substrate that has not been completely etched, unetchedarea 180, and the relationship between surface voltage 240 of FIG. 2 andselectable reference voltage 120 in an area of a semiconductor substratethat has been completely etched, etched area 190. In the unetched area180, which is related to FIG. 1, the etching process has not cleareddielectric 150 from contact site 160. As shown in FIG. 3A, in theunetched area 180, surface voltage 140 is greater than selectablereference voltage 120, and as shown in FIG. 3B, endpoint detectionsignal 170 is at a low level. In etched area 190, which is related toFIG. 2, the etching process has cleared dielectric 250 from contact site260. Also, as shown in FIG. 3A, in etched area 190, surface voltage 240is less than selectable reference voltage 120, and as shown in FIG. 3Bendpoint detection signal 270 is at a high level. Endpoint detectionsignal 170 may be implemented in positive logic as in FIG. 3B or innegative logic, in which case the polarity of endpoint detection signal170 is complemented.

[0033] In operation, surface voltage 140 and surface voltage 240stabilize after the etching process completes. In some manufacturingprocess environments, stabilization occurs a few minutes aftercompletion of the etching process, while in other environmentsstabilization may not occur for an hour or more after completion of theetching process. The actual stabilization time is determined empiricallyfor each process etch step in the manufacturing of a particular productand may depend on environmental factors. After stabilization, system 100measures surface voltage 140 as shown in FIG. 1 or surface voltage 240as shown in FIG. 2. After the measurement is taken, system 100 comparesthe measured value to selectable reference voltage 120. Selectablereference voltage 120, of FIG. 2, is set to a value that can be obtainedempirically and is related to the surface voltage 240 of the dielectric250 when the contact site 260 is cleared of the dielectric. If thecontact site 160, of FIG. 1, is not cleared of the dielectric, then, asillustrated in FIG. 1, the endpoint detection signal is maintained at alow level. If the contact site 260, of FIG. 2, is cleared of thedielectric, then, as illustrated in FIG. 2, the endpoint detectionsignal 270 assumes a high level, indicating that the dielectric etchingprocess completed successfully. An advantage of system 100 is that atthe completion of the dielectric etching process, system 100 makesdetermining the success or failure of the process relatively easy.

[0034] An embodiment of a method in accordance with the presentinvention is shown in FIG. 4. Method 400 for identifying the completionof a dielectric etching process includes setting 410, measuring 420,comparing 430, and identifying 440 operations. In the setting 410operation, a selectable reference voltage is set to a surface voltagevalue, which indicates that the dielectric at the contacts is cleared.In the measuring 420 operation, a voltage probe measures the surfacevoltage of the dielectric after the dielectric etching process in orderto obtain the value of the surface voltage prior to the comparing 430operation. The measuring 420 operation is preferably performed after thesurface voltage has stabilized following the etching process. Thesurface voltage, after the etching process, is an indicator of whetherthe etching process completely etched the dielectric at the contactsite. In the comparing 430 operation, the measured surface voltage iscompared to the selectable reference voltage. And in the identifying 440operation, when the measured voltage is less than the selectablereference voltage, an indicator of whether the dielectric etchingprocess completed successfully is generated.

[0035] An advantage of this embodiment is that it can be tailored todielectric etching steps at any point in the manufacturing process. Thisis accomplished by determining the reference voltage for a given processthrough measuring the surface voltage after the completion of theprocess and stabilization of the surface voltage, and by verifying thatthe contact site is cleared. One method of verifying that the contactsite is cleared is to observe the contact site using a scanning electronmicroscope.

[0036] An alternate embodiment of the present invention is shown in FIG.5. The method includes setting 510, measuring 520, averaging 545comparing 530, and identifying completion 540 operations. As will berecognized by those skilled in the art, it is possible for a singlemeasurement to be in error. So, for the purpose of increasing theaccuracy and reliability of the measurement of the surface voltage, theembodiment shown in FIG. 5 adds the averaging 545 operation foraveraging multiple surface voltage measurements. The number ofmeasurements to average may be determined empirically using methodsknown in the art.

[0037] In another embodiment of the present invention, a furtherimprovement in the surface voltage dielectric measurement process isachieved when the measurements are made at multiple locations on thedielectric. As will be appreciated by those skilled in the art, localprocess variations in the semiconductor manufacturing process are commonand can be accounted for by making multiple measurements at differentlocations on the surface of the substrate.

[0038]FIG. 6 shows a general flow diagram of method 600, a real timeembodiment of the present invention. An advantage of the embodiment ofmethod 600 is that time is not wasted making measurements aftercompletion of the dielectric etching process. Method 600 comprisesplacing 610, setting 620, etching 630, measuring 640, generating 650,detecting 660, and stopping 670 operations.

[0039] Referring to FIG. 6, the placing 610 operation requires placing asubstrate having a dielectric to etch within a plasma etch chamber. Thesetting 620 operation requires setting a selectable reference voltage asdescribed in the previous embodiments of the invention. In oneembodiment of the present invention, the selectable reference voltage isset to a value approximately equal to the surface voltage of thedielectric when a contact site is cleared of the dielectric. The etching630 operation requires etching the dielectric in the plasma etchchamber. The measuring 640 operation requires measuring the surfacevoltage of the dielectric. Any method known to those skilled in the artfor measuring a surface voltage in real time is suitable for use inconnection with the present invention. The generating 650 operationrequires generating an endpoint detection signal when the measuredsurface voltage is less than the selectable reference voltage. Theendpoint detection signal is generated by a comparator as described inthe previously described embodiments of the invention. The detecting 660operation requires detecting the endpoint detection signal. In apositive logic system, the endpoint detection signal is detected byidentifying the time when the endpoint detection signal goes positive.The stopping 670 operation requires stopping the etching process whenthe endpoint detection signal is detected. Purging the plasma chamber orremoving the substrate from the plasma etch chamber stops the etchingprocess.

[0040]FIG. 7 shows a measurement system 700 for measuring the surfacevoltage or a substrate current of substrate 715 in plasma etch chamber705 using probe 710. The present invention can be practiced inconnection with a variety of embodiments of probe 710. For example, inone embodiment, probe 710 is a voltage probe, in another embodimentprobe 710 is a circuit capable of sensing current or the rate of changeof a current signal, in still another embodiment probe 710 is an ammeteror a calibrated ammeter, and in yet another embodiment probe 710 is acomputer system capable of measuring current or the rate of change of acurrent signal.

[0041] Various embodiments of processes and systems for measuring thesurface voltage have been described above. Some of these processes andmethods can be used in connection with the measurement of a surfacevoltage of semiconductor substrate 715. Measurement system 700 has theadvantage that semiconductor substrate 715 is not removed from plasmaetch chamber 705 before making a surface voltage measurement, andtherefore reduces the overall manufacturing time for the substrate.

[0042] Referring to FIG. 8A, in current sensing system 800, plasma ions803 are capable of inducing a current 806 in substrate 809. Substrate809 is not limited to a particular material. In one embodiment,substrate 809 is a semiconductor, such as silicon. In an alternateembodiment, substrate 809 is gallium arsenide. As long as the pluralityof contacts, such as contact 812 and contact 815, are not cleared ofmaterial 818, current 806 is likely to be relatively small, in the rangeof picoamperes. Current 806 is sensed by current sense device 821, whichcan assume a variety of embodiments. For example, current sense device821 can be a circuit, an ammeter, a calibrated ammeter, or a computersystem capable of sensing current. Material 818 is generally adielectric. Types of dielectrics suitable for use in connection with thepresent invention include oxides, nitrides, borophosphosilicate glasses(BPSG), silicon-dioxides, silicon-nitrides, andtetra-ethyl-ortho-silicates (TEOS).

[0043] Referring to FIG. 8B, in current sensing system 823, as contacts827 and 830 are cleared, substrate current 833, which is induced byplasma ions 836, increases to a relatively large value in the range ofmicroamperes or milliamperes. This current can be measured using currentsense device 839. In one embodiment, current sense device 839 is acircuit. In another embodiment, current sense device 839 is an ammeter.In yet another embodiment, current sense device 839 is a computer systemcapable of sensing current.

[0044] Referring to FIG. 8C, a substrate current versus time graph 841shows the increase in current along line 844 as time changes from thebeginning of an etch process at time zero 847 until etch finish time850. At etch finish time 850, the rate of change of the currentapproaches zero. In one embodiment of the present invention, this rateof change is detected to identify etch finish time 850. In an alternateembodiment, etch finish time 850 is detected by empirically determiningthe current value at which the etch process is complete. Substratecurrent at etch process time zero 847 is on the order of picoamperes andat etch finish time 850 substrate current is on the order ofmicroamperes or milliamperes. As described above, the substrate currentvalue at etch finish time 850 is determined by etching a substrate,measuring the substrate current, and verifying that the contacts arecleared using a scanning electron microscope.

[0045] It is to be recognized that the above description is intended tobe illustrative, and not restrictive. Many other embodiments will beapparent to those of skill in the art upon reviewing the abovedescription. The scope of the invention should, therefore, be determinedwith reference to the appended claims, along with the full scope ofequivalents to which such claims are entitled.

Conclusion

[0046] The identification by the applicant of the relationship betweenthe dielectric etching process and the surface voltage, and the realtime relationship between the dielectric etching process and thesubstrate current, permits the above described embodiments of thepresent invention. The embodiments exploit the process insight that as acontact site is cleared of dielectric, the surface voltage of thedielectric decreases, and that in real time as a contact site is clearedof dielectric, the substrate current increases.

[0047] Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement which is calculated to achieve the same purpose maybe substituted for the specific embodiment shown. This application isintended to cover any adaptations or variations of the presentinvention. Therefore, it is manifestly intended that this invention belimited only by the claims and the equivalents thereof.

What is claimed is:
 1. A system for identifying completion of adielectric etching process on a semiconductor substrate having adielectric, and the dielectric having a surface voltage, the systemcomprising: a voltage probe for measuring the surface voltage of thedielectric to produce a measured voltage; and a comparator for comparingthe measured voltage to a reference voltage.
 2. The system of claim 1,wherein the voltage probe is a non-contact probe.
 3. The system of claim1, wherein the comparator is an analog comparator.
 4. The system ofclaim 1, wherein the comparator is a digital comparator.
 5. The systemof claim 1, wherein the reference voltage is set to a valueapproximately equal to the surface voltage of the dielectric when thecontact is cleared of the dielectric.
 6. A method for identifying thecompletion of a process for etching a dielectric on a semiconductorsubstrate having a contact comprising: setting the reference voltage toa value related to the surface voltage of the dielectric when thecontact is cleared of the dielectric;. measuring the surface voltage ofthe dielectric to generate a measured voltage; comparing the measuredvoltage to the reference voltage; and identifying completion of theprocess for etching the dielectric, completion occurring when thecomparator indicates that the measured voltage is less than thereference voltage.
 7. The method of claim 6, wherein the referencevoltage is set to a value approximately equal to the surface voltage ofthe dielectric when the contact is cleared of dielectric.
 8. The methodof claim 6, wherein measuring the surface voltage of the dielectricconsists of averaging multiple measurements of the surface voltage ofthe dielectric.
 9. A method for etching a dielectric having a surfacevoltage on a semiconductor substrate having a contact in a plasma etchchamber, the method comprising: placing the semiconductor substratehaving a dielectric to etch within a plasma etch chamber; setting areference voltage to a value related to the surface voltage of thedielectric when the contact is cleared of the dielectric; etching thedielectric in the plasma etch chamber; measuring the surface voltage ofthe dielectric to generate a measured voltage; generating an endpointdetection signal when the measured voltage, which is influenced by thedielectric thickness, is less than the reference voltage; detecting theendpoint detection signal; and stopping the etching when the endpointdetection signal is detected.
 10. The method of claim 9, wherein thereference voltage is set to a value of approximately equal to thesurface voltage of the dielectric when the contacts are cleared of thedielectric.
 11. A system for identifying completion of a dielectricetching process comprising: a plasma etch chamber; a semiconductorsubstrate having a dielectric, the dielectric having a surface voltage,and the substrate is located in the plasma etch chamber; a voltage probefor measuring the surface voltage to produce a measured voltage; and acomparator for comparing the measured voltage to a reference voltage.12. The system of claim 11, wherein the voltage probe is a non-contactprobe.
 13. The system of claim 11, wherein the comparator is an analogcomparator.
 14. The system of claim 11, wherein the comparator is adigital comparator.
 15. The system of claim 11, wherein the referencevoltage is set to a value approximately equal to the surface voltage ofthe dielectric when the contact is cleared of the dielectric.
 16. Asystem for identifying completion of a dielectric etching process on asemiconductor substrate having a dielectric and a contact, the systemcomprising: a non-contact Kelvin Probe for measuring a surface voltageof the dielectric; and an electronic integrated circuit comparator forcomparing the measured voltage, which is influenced by the dielectricthickness, to a reference voltage set to a value approximately equal tothe surface voltage of the dielectric when the dielectric is clearedfrom the contact, and producing an endpoint detection signal when themeasured voltage is less than the reference voltage, the endpointdetection signal indicating completion of the dielectric etchingprocess.
 17. A system for identifying completion of an etching processcomprising: a plasma etch chamber; a substrate in the plasma etchchamber; and a circuit coupled to the substrate and operable foridentifying when a substrate current exceeds a particular value.
 18. Thesystem of claim 17, wherein the particular value is the substratecurrent at a time when a plurality of contacts is cleared.
 19. Thesystem of claim 17, wherein the circuit is capable of operating during aplasma etching process.
 20. A system for identifying completion of anetching process comprising: a plasma etch chamber; a substrate having amaterial layer having a plurality of contacts, the substrate is locatedinside the plasma etch chamber; and a circuit coupled to the substrateand operable for identifying when a substrate current exceeds aparticular value.
 21. The system of claim 20, wherein the particularvalue is a value of the substrate current at a time when the pluralityof contacts is cleared of the material.
 22. A system for identifyingcompletion of an etching process comprising: a plasma etch chamber; asubstrate having a material layer having a plurality of contacts, thesubstrate is located inside the plasma etch chamber; and an ammetercoupled to the substrate and calibrated to indicate a substrate currentat which the etching process is complete.
 23. The system of claim 22,wherein the ammeter is calibrated to indicate the substrate current atwhich the plurality of contacts is cleared of the material.
 24. A systemfor identifying completion of an etching process comprising: a plasmaetch chamber; a substrate having a material layer having a plurality ofcontacts, the substrate is located inside the plasma etch chamber; and acomputer system coupled to the substrate and operable for identifyingwhen a substrate current exceeds a reference current.
 25. The system ofclaim 24, wherein the reference current is the substrate current atwhich the plurality of contacts is cleared of the material.
 26. A systemfor identifying completion of a dielectric etching process comprising: aplasma etch chamber; a substrate having a dielectric layer having aplurality of contacts, the substrate is located inside the plasma etchchamber; and a circuit coupled to the substrate and operable foridentifying when a substrate current exceeds a particular value.
 27. Thesystem of claim 26, wherein the particular value is the substratecurrent at which the plurality of contacts is cleared of the dielectric.28. A system for identifying completion of a dielectric etching processcomprising: a plasma etch chamber; a substrate having a dielectric layerhaving a plurality of contacts, the substrate is located inside theplasma etch chamber; and an ammeter coupled to the substrate andcalibrated to indicate a substrate current at which the dielectricetching process is complete.
 29. The system of claim 28, wherein theammeter is calibrated to indicate the current at which the plurality ofcontacts is cleared of the dielectric.
 30. A system for identifyingcompletion of a dielectric etching process comprising: a plasma etchchamber; a substrate having a dielectric layer having a plurality ofcontacts, the substrate is located inside the plasma etch chamber; and acomputer system coupled to the substrate and operable for identifyingwhen a substrate current exceeds a particular value.
 31. The system ofclaim 30, wherein the particular value is the substrate current at whichthe plurality of contacts is cleared of the dielectric.
 32. A methodcomprising: placing a substrate in a plasma etch chamber; etching thesubstrate; measuring a substrate current; and stopping the etching whenthe substrate current stabilizes.
 33. A method comprising: placing asubstrate in a plasma etch chamber; etching the substrate; measuring asubstrate current having a rate of change; stopping the etching when therate of change of the substrate current is substantially zero.
 34. Amethod comprising: placing a substrate having a layer to etch in aplasma etch chamber; etching the layer; measuring a substrate current;and stopping the etching when the substrate current stabilizes.
 35. Amethod comprising: placing a substrate having a layer to etch in aplasma etch chamber; etching the layer; measuring a rate of change of asubstrate current; and stopping the etching when the rate of change ofthe substrate current is approximately zero.
 36. A method comprising:placing a substrate having a layer to etch in a plasma etch chamber;etching the layer; measuring a substrate current; and stopping theetching when the substrate current exceeds a predetermined referencevalue.
 37. A method comprising: placing a substrate having a dielectriclayer to etch in a plasma etch chamber; etching the dielectric layer;measuring a substrate current; and stopping the etching when thesubstrate current stabilizes.
 38. A method comprising: placing asubstrate having a dielectric layer to etch in a plasma etch chamber;etching the dielectric layer; measuring a rate of change of a substratecurrent; and stopping the etching when the rate of change of thesubstrate current is substantially zero.
 39. A method comprising:placing a substrate having a dielectric layer to etch in a plasma etchchamber; etching the dielectric layer; measuring a substrate current;and stopping the etching process when the substrate current exceeds apredetermined reference value.
 40. A method for etching a dielectric ona semiconductor substrate having a contact in a plasma etch systemcomprising: placing the substrate having a dielectric to etch within aplasma etch chamber; setting a reference current to a value related to asubstrate current when the contact is cleared of the dielectric; etchingthe dielectric in the plasma etch chamber; measuring the current in thesubstrate; generating an endpoint detection signal when the measuredcurrent is greater than the reference current; detecting the endpointdetection signal; and stopping the etching when the endpoint detectionsignal is detected.
 41. The method of claim 40, wherein the referencecurrent is set to a value approximately equal to a substrate currentwhen the contacts are cleared of dielectric.